Polymers are useful materials because of their ease of fabrication, moldability, light weight, chemical inertness, and low cost. Additional structural applications are limited since polymers are inherently soft materials with relatively low mechanical strength and abrasion resistance. To alter these properties, cross-linking methods utilizing chemical reactions (e.g., thermoset or vulcanized rubber), x-rays, or electron beams, have been employed for some time. Recently, superior improvements in surface mechanical properties have been achieved by implantation of energetic light ions into polymers. In ion implantation, ions are accelerated and extracted from an external source and injected into the surface of a target polymer. Implantation results in modified molecular structures (e.g., 3-dimensional crosslinking) and compositional changes (e.g., hydrogen depletion). Dramatic increases in hardness of up to 44 times, increases in electrical conductivity of up to 10 orders of magnitude, and improved gas permeability of up to 100 times, have been observed. These improvements have been achieved with light ions with energies of order 0.1-1 MeV, and implanted doses of order 10 .sup.15 ions/cm.sup.2. In contrast to electrons or photons, energetic ions are desirable since they produce sufficient linear energy transfer (LET) into electronic stopping (dE/dx).sub.el, which is large enough to result in significant cross-linking within the polymer. During implantation, adjacent hydrogen-carbon bonds in polymer chains are broken by the ion LET. The hydrogen recombines into a gas, eventually diffusing out of the polymer. Free carbon radicals located on adjacent polymer chains subsequently combine to form new C--C bonds, resulting in carbon rich, highly cross-linked polymer chains. To break adjacent C--H bonds, one requires an electronic LET ##EQU1## where .epsilon. is the binding energy (about 4 eV), .delta. is the interatomic spacing, which for many polymers is of the order of about 1 .ANG., and a is a numerical factor, greater than unity, which accounts for other reactions with polymer electrons which lead to ion slowdown but do not result in the breaking of C--H bonds. Assuming a is about 3, one needs (dE/dX).sub.el of 12 eV/.ANG. or more.
A fundamental limitation to the ion implantation process is that since the ions are injected from an external source, only an outer surface of the polymer, corresponding to the projected ion range, R.sub.p (typically.ltoreq.10 .mu.m, for most ions with energies below 1 MeV), can be treated. In many applications, deeper modified layers are desirable, especially for wear applications where plastic deformation of the soft substrate severely restricts the effectiveness of the much harder ion-implanted surface.
It is an object of the present invention to provide a process of treating polymers with neutron capture induced radiation.
It is a further object of the invention to provide precursor compositions for treatment by neutron capture induced radiation.
Still further, it is an object of the present invention to provide the altered polymeric products of neutron capture induced radiation.